human-powered peanut thresher for small scale … · human-powered peanut thresher for small scale...

Human-Powered Peanut Thresher for Small

Scale Zambian Farmers

Alex Caine, Oscar Castro, Cody Lange, Ashley Wilkey

ME 491

Dr. Thompson

December 9, 2016

Executive Summary

Human-Powered Peanut Thresher

International Humanitarian Design

1

Students enrolled in ME 491 International Humanitarian Engineering, taught by

Dr. Brian Thompson, assembled into teams of four in order to successfully complete a

semester-long design project.This project is continuing the development of a previous

ME 491 project by Adam Lyman. His team created a bean thresher that has been

successfully prototyped in Zambia. Our project description states “design and

manufacture a modular peanut threshing machine that can be used by small-scale

farmers in Zambia to de-shell and separate peanuts from their husks.”

On the current bean thresher design, four variables could be adjusted in order to

create a compression and shear force necessary to break open a peanut. An

experiment was created to test the effect of threshing when different rubber and sheet

metal surfaces were attached to the drum and concave. Also, different surface speeds

were tested, and distances between the concave and the drum.

Results from this experiment led to the selection of a material that was

manufactured to be fitted onto the existing bean thresher. Mechanization of the peanut

threshing process will allow small-scale zambian farmers to produce more output. In

turn this will give the women of Zambian more time to focus on education, health, and

family.

Table of Contents :

Project Introduction 3

Design Parameters 6



2

Weighting Factors 7

Function & Performance 8

Product Cost 10

Delivery Date 10

Quantity 11

Safety 11

Quality 12

Energy Consumption 12

Reliability 13

Maintenance 13

Mechanical Loading 13

Size 14

Weight 14

Spatial Constraints 14

Aesthetics 15

Transportation & Packaging 15

Personnel and Human Factors 15

Service life and Shelf Life 16

Noise Radiation and Environmental Issues 16

Operating Instructions 16

Health Issues 17

Government Regulations 17

Operating Costs 18

Environmental Conditions 18

Introduction into Design Phase 18

Peanut Thresher Designs 19

Duplication Design 20

Combination of Belt and Drum Threshing 21

Swinging Rods Threshing 23

Empathy 25

Brainstorming 27

Checklists 28

Analogy 30

Biomimetics 31

Decision Matrix 32

Experiment 33

Setup 34

Procedure 36

Results 37



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Fin Design 37

Smooth Rubber Design 37

Scale Design 38

Metal Punch-Star Design 39

Metal Punch-Rows Design 39

Metal Punch-Star 40

Manufacturing 41

Conclusion 44

Bibliography 45

Appendices 46

Project Introduction

Zambia is a landlocked country located in the center of Africa as shown in figure

1. Currently, Zambia has a population of around 11.2 million people. Life expectancy in

Zambia is only 41 years old (National Geographic). Zambia is currently considered to be

the Least Developed Country by the United Nations. Countries present on the list of

Least Developed Countries, “comprise more than 880 million people (about 12 per cent

of world population), but account for less than 2 percent of world GDP and about 1

percent of global trade in goods.”



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Figure 1. A map of Zambia.

Currently there has been an increase in agricultural development to help lessen

the struggles with malnutrition and starvation in Zambia. Agricultural development is

done by primarily two methods. The first method is improving practices such as

increasing seed varieties. This has been the primary approach being implemented by

NGO’s. Although there is more yield being produced, they are now lacking the

machinery to process the crops.

This device will use the second method, which is introducing technical

equipment to reduce labor time. Most of the farm labor is performed by the women. If

mechanization can be introduced successfully, women would be able to spend saved

time to focus on education, health, family, and much more.

Our project will be contributing to current Michigan State University research

trying to introduce mechanization to small-scale farmers in Zambia. Right now there is a

threshing machine system being tested in Zambia which is powered by developing



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universal pedal power take-off. This machine can process common beans but not

peanuts. Peanuts are relatively soft compared to the beans. When the peanuts are ran

through the bean thresher they become broken, and are no longer acceptable to be sold

in the market.

As a team, we are to design a peanut thresher that can dehusk peanuts with no

defects for small scale farmers in Zambia. Peanuts are a popular crop in the northern

region of Zambia.Farmers in Zambia rely on these peanuts for a source of nutrition and

income. If there are defects in the peanuts they will not be accepted to sell in the

market. This can be detrimental to farmers considering that some people in Africa are

surviving on less than two U.S. dollars a day with seventy percent of Zambians living in

poverty.

Even though peanut threshers have been developed in Zambia, the people have

not adapted them into common farming practices. Our team needs to design a new

innovative peanut thresher. Along with the task of diffusing the innovation so that it can

be accepted by the farmers in Zambia. Cultural traditions will be taken into account

when attempting to introduce the peanut thresher device, and Adam Lyman will be

working on how to integrate these thresher into the lives of these women farmer.

Without the acceptance from the farmers, there is no functionally project. As seen with

other threshers, natives may be reluctant to accept the technology but it is a risk that is

necessary.

Design Parameters



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It is impossible to design anything without first knowing the design specification.

A design specification is a way of clearly defining the problem that needs to be solved.

Without this knowledge there would be no foundation for the purpose of the design, and

its possible that the device created won’t solve the problem presented.

To specify a design there must be defined design parameters. Design

parameters imposes constraints on the design. This is a very necessary step in the

designing process because if a problem is not properly defined it can not be properly

solved. Table 1 lists common design parameters that need to be taken into account

when designing our peanut thresher.

Table 1. Common design parameters taken into account for our device.



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Weighting Factors

Each design parameter needs to be evaluated on how essential it is to the

design. This can be done through assigning each parameter an importance factor

ranging from three to zero as shown in Graph 1.

Giving a design parameter a score of three would indicate that it is essential to

the design and if not satisfied completely would make the threshing device

unsuccessful. Assigning a design parameter a value of two would mean that its is highly

desirable and needs to also be met in the design. Design parameters given a one are

desirable, and should be taken into account when designing but does not need to be

present in the design. Parameters given a evaluation of zero are almost irrelevant when

creating our peanut thresher.



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Graph 1. Above shows each design parameters importance factor assigned

by the team.

Function & Performance

Currently, farmers are able to de-shell peanuts by hand at a rate of 10 kg

per hour. This is a very time consuming-process, and these women do not have time to

invest in their education, health, and socio-economic status. Adam made it clear that the

peanut thresher needs to output 100 kg of peanuts per hour within the tolerances of -5

kg of peanuts per hour.

Our thresher will need to be compatible with an already existing bicycle mount.

This mount was created only for the buffalo bicycle. Pedaling the buffalo bicycle should

input 100 W of power to our peanut thresher. An issue could arise with pedaling for

inputting power because farmers could be using this machine for eight or more hours at



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a time. To solve this issue another group is designing a platform to power our peanut

thresher. We need to callibratorate with this group to make sure their design can

properly run our peanut thresher.

The product of this machine needs to be a sellable peanut at the customer's local

market, meaning that the peanut gets separated from its shell and remains perfectly

intact.Figure 2 shows peanuts that would not be sold in the market. Out of 100 kg of

peanuts threshed per hour, the team is shooting to reduce the amount of unsellable

peanuts to less than three kg/hr. This parameter was given a 3 because creating a

functional and successful device is the whole point of the project.

Figure 2: Unacceptable groundnuts to be sold in the market place.

Product Cost

Our team was given a budget of $500 to develop a prototype for peanut

threshing. This parameter was given a 3 because Michigan State University and the



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Zambian farmers that we are building the device for do not have infinite funding to

develop this device.

Delivery Date

Design Day, or December 9th, 2016, is the deadline for this project. This

parameter was given a 3 because, otherwise, everyone in this team would likely fail ME

491 and our opportunity to change the world would be a waste. Adam Lyman also

wants to be able to use this prototype for the harvest season of 2017 which is another

reason why the delivery date is set as is.

Quantity

Ultimately, by the end of 2018, the final model of the peanut thresher will

be replicated 12 times by a company that is not yet known. For this class, however, the

team is only concerned with designing and developing the initial prototype, so this

parameter was only given a one.

Safety

Safety is always a priority, regardless of the fact that this is supposed to

be an economical machine. Hence, this parameter receives a 3. Safety is one of the

most important measurements in any project. We took into considerations the lives and

the well-being of the women farmers that will have to operate this peanut thresher. On



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average the operator will weigh any where from 130 to 180 lbs, and be 16-70 years of

age.

Quality

By the end of the fall 2016 semester, the team needs to have a visually

appealing, working, and economical prototype that can easily be tweaked into a

production model. Also, the peanut thresher needs to thresh peanuts into something

that can actually be sold. High quality is the goal, so this parameter gets a 3. Quality

can be defined as the peanut thresher outputting 100 kg of peanuts per hour for a

minimum of one harvest season. Zambians will most likely not understand the

importance of maintenance for the device. For this reason to maintain high quality of our

peanut thresher there needs to be little to no maintenance required.

In the words of Adam, “Imagine when you hand shell a peanut. As soon as you

uncrack the shell, there are two "whole nuts" inside, three if you get a special one. That

is what you need to aim for in the machine design.” In worst case scenarios, the broken

peanuts are deemed “bad” by the farmer are usually thrown away. Instead of throwing

away the broken peanuts the small-scale farmers of Zambia can benefit from starting a

business of making peanut butter with the “bad” peanuts.



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Energy Consumption

100 watts of power or less is required to run this machine. Right now there

is threshing machine system being tested in Zambia which is powered by developing

Universal Pedal Power Take-off. Our design should use this same powering method for

our device. This is a very important parameter, but because this does not yet seem like

a challenging goal, this parameter gets a 2.

Reliability

This specific peanut thresher must be able to last 10 harvest seasons. The

peanut thresher is expected to operate successfully and reliably, meaning that the

thresher will not need major maintenance from non-local fabricators. This parameter is

assigned a 2.

Maintenance

Local fabricators need to be able to repair the machine, should anything

happen to it during the harvest.Average tooling found in a toolbox should be enough to

repair any and all parts within the product. Maintenance must also be done on the bike

to retain its aesthetically pleasing design and display. This parameter is assigned a 1.

Mechanical Loading

Wood will be avoided for structural support in the final design. In the

prototyping phase, wood can be used for pulleys and other minor components.Standard



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stock material will be used, for the most part. Using acceptable materials is essential to

both the function and budget, so this parameter gets a 2.

Size

General dimensions are 3 ft wide, by 3 ft. deep, by 3 ft. tall, and the

machine needs to fit on the back end of the buffalo bicycle on a mounting system. If the

machine does not fit, the project can be considered a failure, so this parameter is

assigned a 3.

Weight

Zambian farmers need to be able to pick up the machine and need to be

able to use it, so 100 kg is the highest mass that the machine can be. Any weight higher

than that would not be beneficial to the farmers as they are responsible for the

transportation of the bike and thresher. This parameter is assigned a 3. The weight is

also a parameter that can be tied in with safety as well. Weight is a factor that must be

analyzed as the farmers do not have unlimited strength after a long day in the field.

Spatial Constraints

This parameter can somewhat be grouped together with size. As stated

before, the thresher must be 3 ft. wide, by 3 ft. deep, by 3 ft. tall. A wheat threshing

mount exists that the peanut thresher needs to be compatible with, and the machine

needs to be able to fit on the back of a bike, so this parameter is assigned a 3.



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Aesthetics

An understanding of tasteful design and Zambian culture is essential to

this project, because the machine needs to be something that the Zambian farmers

actually want to use. This parameter gets a 1. Adam Lyman will be diving deeper into

the understanding of Zambian culture and will be prototyping and collecting real data

from the farmers.

Transportation & Packaging

Zambian farmers will be transporting the bike from farm to farm via the

bike that the machine is mounted on. Due to this specific manner of transportation, the

team needs to be able to keep the weight of the thresher much below 100kg. This

parameter gets a 1. It is expected for the farmer to not travel in weather that may be

detrimental to the bike and its functionality.

Personnel and Human Factors

Our team will be dealing with customers that range from a 130 lb., 16 yr.

old male or female to a 180 lb., 70 yr. old male or female. Average heights of Zambians

are similar to the average heights of Americans, if not slightly shorter, and the machine

should be designed such that a person with a height of 5 ft. 2.5 inches can load the

machine. It is crucial that the Zambian farmers are actually able to use this machine, so

this parameter gets a 3. The human factors that are foreseen with this thresher are the

education level of the farmer, that only needs to know how to ride a bike. Dress code for



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the farmers, as most of the farmers will be women and they wear long dresses. Lastly,

due to the multiple kids that may be around while the thresher is in use, the team must

also take into the account the possibility of kids playing with or around the peanut

thresher.

Service life and Shelf Life

As mentioned before with reliability, this specific thresher must be able to

last 10 harvest seasons and must be able to maintenanced by local fabricators using

the contents of a regular toolbox. When not in use, five years is our initial goal.This

parameter gets a 1.

Noise Radiation and Environmental Issues

There are no parts of this specific thresher that will violate any EPA or

OSHA Regulations. The noise radiation from the thresher must not exceed 90 dB. The

team must also take into account the different environments the product will be placed

in, thus surfacing possible mouth and eye protection while the thresher is in use. This

parameter is assigned a 1.

Operating Instructions

Riding a bike that will automatically thresh the peanuts for the operator is

a task that is known by the farmer so there will not be a need to create operating

instructions for the bike, so this parameter gets a 1. Instructions for the loading and the



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collection of the peanuts will be created. Any instructions needed for the farmer will be

in English, as deemed by Adam.

Health Issues

With the exception of any potential safety hazards, the prototype is not

expected to pose any health issues. This parameter gets a 1. Adam also stated, “No

particular health issues outside the obvious emphasis on safety.” The team will take

into account the well being of the farmer and will take into account the work day, to

ensure the bike does not require any work that could potentially cause short term or

long term health issues for the farmer, such as wear and tear on the body and muscle.

The team, as stated before, will also take into account the need for eye and mouth

protection for the farmer using the thresher and the farmers that could possibly be

around the thresher while in use.

Government Regulations

After reviewing official documents and regulations, there are no government

regulations that will be violated in either the United States or in Zambia. This parameter

is assigned a 1.

Operating Costs

The bike must be able to generate 100 watts for the thresher to operate at

its maximum capacity. The farmer must be able to produce these watts solely from the



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bike itself. These 100 watts will help the operator produce 100 kg of peanuts rather than

the 40 kg that they are producing with other threshers. This parameter is assigned a 1.

Environmental Conditions

Although difficult to predict, dust storms and possibly rain at times are the

harshest conditions that the thresher needs to be able to operate in. Because this

parameter is related to its performance, this parameter gets an importance factor of 2.

The team will also consider the implications of the design, such as the possible

production dust storms and flying particles.

Introduction into Design Phase

The best kind of design phase of any project is one that produces multiple ideas

from the different minds available. As Linus Pauling once said, “The best way to have a

good idea is to have a lot of ideas”. After the creation and careful analysis of the design

parameters, the peanut threshing team was able to enter the design phase to create a

conceptual design.

There are 3 different types of conceptual designs, first suggested by Pahl and

Beitz, these three are named, Original Design, Variant Design, and Adaptive Design.

Original is where “a radically new product or concept is created”. Variant is when the

“size or configuration of a product is changed but the operating principle and the

function remain unchanged”. Adaptive design is defined as “a product is changed to

solve a different problem but the original operating principle remains unchanged”. The

project requires an adaptive design as the idea of threshing peanuts came from a

previous project based on threshing regular beans.



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Following a discussion with the team collaborator, Adam Lyman, the team was

set on the path to conceptualize and build a working drum for the thresher. Along with

the design of the actual drum, the team was also tasked with testing and optimizing the

speed necessary to thresh the peanuts correctly.

Each team member produced two different ideas each. All ideas were created

using different methodologies to maximize innovation and creativity. Methodologies

acted as guidelines to allow the team members to dive deeper in creativity. The different

methodologies used were Historical, Combination, Duplication, Biomimetic, Empathy,

Brainstorming, Analogy and Check List.

After all conceptual designs were created, the team members used a design

matrix to rank and find the “best” idea. Multiple tests and prototypes are in the

immediate future for the team. All prototypes will be created using the best designs

seen in this report.

Peanut Thresher Designs

Designs were generated by the team for different drums that will be evaluated for

the final peanut thresher design. A threshing drum is the cylinder in the center of a

thresher that rotates to break the shell away from the peanuts. The concave of the

thresher is the cover for the drum that traps the peanuts against the rotating drum. Both

of these components can be viewed in figure 4 below.



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Figure 4. Drum and Concave Locations on Thresher

Duplication Design

Figure 5: Duplication Design of a Drum

This drum design will have threaded holes along the whole body of the cylinder

to allow for exchangeable rubber attachments of different shapes to be tested as shown

in Figure 5. Each different type of attachment can be screwed into each threaded hole

of the thresher in order to obtain proper function. Individual attachments will be made of

rubber in order to create a less forceful process to keep the quality of the groundnuts up

Drum

Concave

Peanut Input



20

the design specification. The drum will be made of sheet metal to support the screwed

in attachments during the threshing process.

An advantage of this design would be its versatility. The team will be able to

quickly produce, and exchange out different drum surfaces. This will allow the team to

evaluate the effectiveness of many ideas without putting all our energy into one single

design.

A strong disadvantage to this design is the amount of time it will take to load it

into the thresher, and attach all of the components. This design will also involve making

a lot of parts which in turn will increase the overall cost.

Combination of Belt and Drum Threshing

There are many different methods that currently exist for threshing a variety of

different crops. Each method has its advantages and disadvantages. This idea was

generated by combining two know threshing methods to try and reap the benefits from

both of them. These methods are belt and drum threshing.

Belt threshing is a process that incorporates two rubber belts that rotate at

different speeds. The top belt rotates in a counterclockwise direction and the bottom belt

rotates in a clockwise direction. This process is typically used on crops that require a

more delicate approach.

Drum threshing utilises a rotating cylinder with a rough surface that grinds the

shell of the crop against a curved wall to separate the seed from the shell. This process

is much more aggressive and can cause the seeds to break during the process.

Advantages of this method is that it has a compact and simplistic design.



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These two processes were combined by taking the rubber surfaces from the

belts and applying them to the drum and the concave walls of a standard drum thresher.

An image of this design can be seen in figure 4.

Figure 6: Drawing of the Combination Design

Rubber surfaces provide the desired delicate touch to extract the peanuts form their

shells without damaging the quality of the peanut. Figure 7 shows the rubber texture

that will be applied to the outer surface of the drum and the concave.

Figure 7: Rubber Applied in Design

Advantages to this design include the delicate threshing approach, the compact

design, and the manufacturability. Unlike most drum threshing designs, the combination

design creates a friction driven process that provides torque to the shell to twist it off. By

Front Side

Rubber Surface

Hollow Steel Cylinder



22

twisting the shell off, the peanuts themselves are never under any pressure and have a

lower chance of cracking. By having the drum instead of the duel belts, the thresher can

function in a smaller space. In addition to these other advantages, this design have very

few parts in its design.

Disadvantages for this design include concave alterations and number of

materials used. By adding material to the inside of the concave, it is adding more

material and steps to the installation process. There will also have to be a design

feature that will temporarily connect the rubber to the concave. Also, there are two

different types of materials used in this design, so cost of this design will be higher.

Swinging Rods Threshing

Evolution of technology can cause tasks to become overly complicated. Looking

back on the history of threshing can provide insight to simple ways of accomplishing this

task. Early forms of threshing involve the beating of shelled seeds with sticks and rocks

in order to expose the seeds. This method is extremely simple and can be integrated

into the advanced drum threshing design.

In the swinging rod threshing design, the drum is attached to a number of beating

rods that can rotate about the connection point between the rods and the drum. By

allowing these rods to have this additional degree of freedom, the rods will be able to hit

the peanuts and recreate a miniature version of the old beating process. Figure 8 shows

the front and side view drawing of the swinging rod design.



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Figure 8: Drawing of Swinging Rod Design

Advantages of this design include that it threshes all peanut shell sizes and that it

will thresh the peanuts at a fast rate. One of the issues that the Zambian farmers are

running into is that threshing peanuts by hand takes far too much time, this is why the

parameter was ranked so high in the previous report. Also, having to change the drum

in the thresher to thresh different sized peanuts is a waste in time and materials.

Disadvantages of this design include aggressiveness, number of parts, and cost

to manufacture. Zambian farmers need the peanuts to be whole, so that they can be

sellable in the market. If the peanut threshing process breaks the peanuts, then the

farmers will be losing money and will not profit off of the improvements in the threshing

process. In addition, adding more parts to the design will make it more likely to fail and

will make it much more expensive to manufacture.

Installation of this drum will involve opening up the bean thresher, sliding the old

drum out, and sliding the new drum in its place. This drum requires no alterations to the

Front Side

Hinged Steel or Wood

Hollow Steel



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concave of the thresher making the exchange simple. Handling this drum design could

also have safety issues due to the fact that it has many moving parts and pinch points.

Empathy

Figure 9: A design for a hollow steel drum coated with rubber is depicted

Safety is a heavily prioritized design parameter, so using the design synthesis

method known as empathy, the concept of making a steel, cylindrical drum that is

coated with rubber and using rubber teeth on the concave was made. A sketch of this

design can be found in figure 9. Zambian operators using this device are at less risk of

suffering a major injury if something gets caught in the thresher, as rubber will do less

damage. A relatively soft surface also minimizes damage to the peanut during shelling,

and hard bristle at the end of the concave helps to complete the separation of the nut

from the shell, so the function and the performance of the machine are actually

improved.

T

Side



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Front Side

Top

Thic

However, the improvement of safety, performance, and quality are at the

expense of other important parameters. Coating the drum with rubber will make the

device more expensive and heavier. Also, the rubber on the device potentially lowers

the reliability of the machine, as the rubber will get worn down faster than steel would.

Maintaining the machine would be more routine and costly.

To build this design, sheet metal needs to be rolled and welded together. Circular

plates are welded to the drum to complete the shape. A strip of rubber teeth is screwed

down to the drum.

Brai

nsto

rmin

g



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Figure 10: A hollow sphere design with steel teeth and bristle fixtures is shown.

When designing an interchangeable drum, a cylindrical shape is often the first

shape that comes to mind. However, using the brainstorming synthesis method, a

hollow, spherical design made of steel was considered, as shown in figure 10. Thick

bristle fixtures are placed along the concave of the thresher so that there are no gaps

for peanuts to fall through, and as the spherical drum rotates around, peanuts of

different sizes are sorted to areas between the drum and the bristles where they fit the

best.

Currently, this design proposes the use of teeth that define the look of a

basketball, as aesthetics are important to customers. In theory, allowing different areas

between the drum and the concave for peanuts of different sizes to go through also

increase the quality of the finished product and bolsters the performance of the

machine.

Disadvantages to this design include that placing the bristle fixtures is an added

step with added costs, and they might not even help the peanuts find where they are

sorted best in the concave or adequately help separate the nut from the shell.

Additionally, manufacturing a spherical drum is more expensive than manufacturing a

cylindrical drum.

To build this design, steel needs to be kneaded between two dies, flash lines

need to be removed with cast iron plates, the drum needs to be heat treated, and a

fixture needs to be placed that connects the drum to the thresher’s main body. Steel

teeth are welded to the drum, and bristle fixtures are screwed to the concave.



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Checklists

Figure 11: Concept drawing of drum based on Checklist methodology

The idea and concept drawing displayed in Figure 11 was a creative idea that

had its roots based in the methodology of Checklist of Questions. A list of questions that

were first produced by A. F. Osborn, allowed the team member to tackle the open-

ended question of the drum design. This type of methodology can also be used in the

detailed design phase of the project, as that is when there is a focus geared towards

hardware considerations.

In this type of drum, the “teeth” would be fins that are straight across the drum,

as displayed in the front view of the figure. Fins would also be present on the inside of

the concave that wraps around the drum. Both sides of fins would minimize the amount

of “bouncing” the peanut does within the concave, which would reduce any damage to

the peanut within the shell. Another advantage of the fins is the ability of threshing

different sized peanuts. Since the fins within the thresher increase in height, any sized

Side Front

Rubbe



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peanut would be caught in the fins, thus reducing the number of peanuts left

unthreshed. Not only are there foreseeable advantages but there are also

disadvantages that can be predicted. Design of the fins could also create pockets where

the peanuts could be caught and could go through the process unthreshed.

Materials necessary for this idea would be sheet metal and rubber. The fins

would be entirely created from rubber. Another concept is having the fins be created out

of sheet metal and have rubber casings over the fins. The fins would be welded, if made

of metal, or the fins would be adhesively bonded or bolted into the sheet metal drum.

Lastly, another concept could be creating the fins using a rubber belt. Having

replaceable belts would allow for different types of teeth to be used with different

peanuts (wet, dry, big, small, etc.) and having replaceable belts would allow for quicker

maintenance of the thresher.

Analogy



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Side Front

Rub

Figure 12: Concept drawing based on Analogy Methodology

Direct Analogy was the methodology used in creating the design in Figure 12.

This type of methodology involves making a comparison of similar techniques,

technologies, or knowledge from different fields. The team member used prior

knowledge and experience with gears and the technique behind them to create a similar

symmetrical design. Just as with the teeth of two gears, the teeth of the drum will align

and fit perfectly with the teeth on the inside of the concave while leaving a pocket for the

whole peanut to exit the process.

With the reduction of pockets and free space within the concave, there will be a

reduction of “bouncing” the peanut goes through. There is also a reduction of peanuts

that go through the system unthreshed, since there will be minimal space between the

teeth of the concave and the drum, all sized peanuts will be caught by the drum.



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Based on the first conceptual design, the material required was metal. After

further review, the teeth could also be produced with rubber material which would

lessen the impact of drum on the peanuts. Fins would either be screwed into the drum

or welded onto the drum. The fins on the inside concave would go through the same

process the drum as the drum. Overall, this idea partially uses a concept used in a

different field and a hint of creativity to try to solve the major issue at hand.

Biomimetics

Figure 13:Biomimetic Drum design

This drum design was inspired by the operation of a raven using its beak to chip

away at the outer shelling of a peanut. As seen in the figure above the peanuts would

drop down into concave while the drum would be rotating and coming into contact with

the peanut imitating the peaking motion of a raven. This entire drum would be made of

metal in order to replicate the hardness of a raven’s beak.

Biomimetic Design



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An advantage of this drum design would the sharp point of the teeth. The point

will be able to catch more easily on the outer shelling of the peanut, and be able to roll

of the roundness of an already unshelled round peanut.

A disadvantage of this drum design would be the complexity of manufacturing the

needed shape for the teeth. Another major drawback would be the needed maintenance

when the teeth would become dull from the continued use of the thresher. Also this

drum design would be hard to load and unload into the peanut thresher because of its

heavy weight compared to other drum designs.

Decision Matrix

Table 2. The decision matrix used to select the top 3 designs is shown.

A decision matrix, as shown in Table 2, was used to determine the most effective

designs for threshing peanuts by assigning ratings for how each design addressed the

most highly weighted parameters described in Progress Report 1. This process resulted

in the top three designs being rubber-based designs. These designs were synthesized

by combining belt and drum threshing, making a checklist of questions, and empathy

best addressed the defined design parameters. Ratings of 1-3 were issued to each



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design for how they addressed each parameter. “1” meaning that the design did not

address the parameter relatively well and “3” meaning that the design met and

exceeded the goals defined by the parameter.

Glaring issues were present with the designs made by the biomimetics, swinging

rods, and duplication methods, especially with the parameters weighing to weight, size,

cost, and maintenance. Not too many issues were apparent with the analogy-based

design, but the combination, checklist, and empathy designs scored better and will be

focused on during the prototyping stage.

Experiment

In order to modify the current bean thresher there was four variables that could

be changed in order to create a more gentler process for threshing peanuts. The

combination of these four variables had to create a compression and shear force on the

peanut in order to get a good quality peanut. This good quality is defined as the

groundnut being whole, and the red film still being attached to the peanut.

First the variable of drum surface could be altered on the existing design. Our

team decided to test two types of surfaces rubber, and sheet metal. Rubber was chosen

because it is less forceful, and these surfaces could be repaired with materials available

to Zambian farmers like bike tires. Sheet metal was chosen as our second surface to be

tested because the team could easily manufacture a hole punch design with materials

available to Zambian farmers including a hammer and nail.



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Another variable to change was the concave surfaces. Both rubber and sheet

metal were also used to attach to the concave. The distances between the drum and

the concave could also be altered to adjust how many peanuts could run through the

thresher. Lastly the surface speed could be adjusted to change the rpm the drum was

rotating. Speeds were tested from 150-920 ft/min.

Setup

In order to test the threshing process the team was able to obtain a 10 year old

thresher from the Crop Barn shown in Figure 14. This thresher was originally created for

wheat threshing, and therefore was too violent for peanuts. In order to run our

experiment the team needed to change this spiked tooth thresher into a thresher that

could be modified to fit our different desired surfaces on both the drum and the concave.

Figure 14: Wheat Thresher obtained from Crop Barn.

First, the team was able to remove the teeth by hammering them off both the

drum and concave. Then it was time to get into the College of Engineering Machine

Shop in order to turn down the diameter of the drum using the lathe. This would allow



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the drum to have a smooth surface for applying our surfaces. To attach the surfaces we

drilled and threaded four holes into the drum. Surfaces on the drum were then able to

be screwed in, and surfaces for the concave were screwed in and bolted.

Figure 15. Attachment of surfaces on the concave and drum.

Originally the wheat thresher was attached to a motor that was not ideal for

testing, and was exchanged with a new motor. In order to get slower speeds a second

power system was implemented for testing. A new platform was also created to allow

for proper placement of the thresher, motor, and pulley system.

Procedure

1. Screw one of the six surfaces shown below into the concave and drum.

Food-Grade White

Styrene Butadiene

High-Strength

Zinc plated 26 gauge





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Incline Conveyor Belting Nitrile

Rubber

Multipurpose Neoprene

row design grid design star design

2. Adjust the speed dial, and use the Tachometer to find the desired speed of 150

ft/min. Tolerances are set to plus or minus 10 RPM.

3. Run two cups of raw,unsalted, and unthreshed peanuts through the thresher.

4. Sort the output into three categories: good quality, bad quality, and unthreshed.

5. Hand thresh the peanuts that were not threshed by the machine.

6. Weigh each category in grams.

7. Record the data.

8. Repeat steps 1-7 using surface speeds of 220, 460, 850, and 920 ft/min

Results

Fin Design

Data that was collected from the experiment was put into bar graphs to compare

how the surface types and surface speeds affect the percentage of good, bag, and not

threshed peanuts. Firstly, the fin rubber design had an exponential increase in percent

of bad quality peanuts as the the surface speed increases as seen in Graph 2. Good

quality also increases with surface speed, but peaks at 850ft/min then decreases.

Overall for this design, the optimal speed was 460 ft/min because it threshed

approximately 25% of the peanuts with good quality and only broke 3%.



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Graph 2: 4.5inch Diameter Drum Fin Design Results

Smooth Rubber Design

Next, the smooth rubber design also had an increase in percent of bad quality

peanuts as the the surface speed increases as seen in Graph 3. Good quality stays

10% and 15% for all of the speeds. Overall, this design’s bad quality to good quality

ratio was high and the surface didn’t thresh enough.

Graph 3: 4.5inch Diameter Drum Smooth Design Results

Scale Design

Lastly for the rubber surfaces, the scale rubber design also had an increase in

percent of bad quality peanuts as the the surface speed increases as seen in Graph 4.

Good quality increases steadily as the surface speed increases. Overall, this design’s



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bad quality to good quality ratio was high and it either didn’t thresh enough or it broke

too many peanuts.

Graph 4: 4.5inch Diameter Drum Scale Design Results

Metal Punch-Star Design

To start the metal surfaces, the star rubber design also had an exponential

increase in percent of bad quality peanuts as the the surface speed increases as seen

in Graph 5. Good quality also exponentially increases as the surface speed increases.

Overall, this design’s bad quality to good quality ratio was high and the ratio remained

the same as the surface speed increased.

Graph 5: 4.5inch Diameter Drum Star Design Results



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Metal Punch-Rows Design

Metal punch with the star pattern had a steady percentage of bad quality peanuts

as the the surface speed increased as seen in Graph 6. Good quality fluctuated

between 10% and 15% with all the surface speeds. Overall, there was not a definitive

best surface speed for this design and none of the results showed a reasonably good to

bad quality ratio.

Graph 6: 4.5inch Diameter Drum Row Design Results

Metal Punch-Star

Lastly for the metal surfaces, the grid design had a steady amount of bad quality

of peanuts as seen in Graph 7. Good quality increases steadily as the surface speed

increases until 460 ft/min then it decreases. Overall, this design’s bad quality is low

compared to the other surfaces. This surfaces best performance is at 220 ft/min.



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Graph 7: 4.5inch Diameter Drum Grid Design Results

After testing was completed on the wheat thresher from the crop barn it was time

to take our best design, and test on the current bean thresher design. First, the team

had to remove the spiked teeth from the bean thresher by taking our each individual

screw and bolt. Our fin design was then manufactured to fit the dimension of the current

bean thresher drum and concave. Surfaces were attached in the same manner as the

smaller thresher, and the testing procedure remained the same. Except to account for

the larger drum size 13” compared to 4” the team ran three cups of peanuts through the

thresher for testing.



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Graph 8: 14 inch Diameter Drum Fin Design Results

Manufacturing

Cost reduction and ease of manufacturing were all taken into consideration when designing and

making the drum surfaces. An emphasis was placed on allowing for simplified assembly and repairing

processes.

For the fin surface, a 6.5”x43.5” strip of food-grade white incline conveyor belting nitrile was

purchased from the McMaster website. Typically, a perfectly sized strip of rubber is not available for sale.

If this appears to be the case, a box cutter can be used to cut the surface down to size. Nine ¼”-20

threaded screw holes exist on the bean thresher already, so holes of the same diameter are drilled into the

fin surface. Locations of these screw holes are indicated in figure 16. A Phillips screwdriver is then used

to attach the surface to the drum with ¼”-20 flathead screws.



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Fig. 16 White dots indicate where the quarter inch holes need to be made.

Fin concave surfaces are also bought from McMaster and attached in the same manner to the

thresher concave, only the concave surfaces are 6.5”x12” and only six ¼” screws are needed to fasten

concave surfaces. Screw holes are still punched from the same relative distance to the ends of the surface,

as shown in figure 17.



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Figure 17. Dimensions and screw hole locations are shown for fin concave surfaces

Fig 18: Properly attached material to concave and drum

Fig. 18 provides a reference of what a properly assembled Thresher and Concave looks like. A concave

with the surface attached is shown on the left, and a drum with the fin surface attaches is shown on the

right.

Once the drum and concave surfaces are attached, the concave must be placed on the hooks that

hold it to the thresher frame, and it must be adjusted by moving the hex nut that constrains the concave’s

movement so that the clearance is 0.875 in. from the peak of a drum fin to the peak of concave fin. This

can be done by adjusting the location of the hex nut on the part of the thresher frame that restricts concave

movement.

It is predicted that fin surfaces will erode significantly over the course of the threshers intended

10 harvest period of use, so either replacement surfaces will need to be purchased and prepared. Another

solution is patch repairs which can be done using household materials. If a patch repair is opted for,

household materials, like the rubber on bicycle tires, can be used to repair the surfaces by cutting the



43

desired piece of rubber and using an adhesive, such as various epoxies, to fill the worn away portion of

the surface.

Conclusion

Through experimental testing our team was able to create an interchangeable

drum and concave surface for peanut threshing. This material is known as food-grade

white incline conveyor belting nitrile. It was obtained through a supplier website called

Mcmaster. Compression and shear forces were best created with this surface, and

adequately produced a good to bad ratio of 7 to 1 peanuts.

Overall introducing this human-powered peanut thresher design to small-scale

farmers in the Northern Province of Zambia will make a profound impact on their lives.

Currently, the farmers are hand threshing at a rate of 1 kg/hr. With mechanization of this

design the farmers will be able to generate an output of 35kg/hr. That is an overall

improvement of 35 times more output.

If a typical Zambian farmer works 8 hours a day they can output 8kg/hr, and

when using this design that same output of 8 kg/hr can be created in 14 mins. This will

allow the farmers to save time with threshing peanuts, and allow for more product to be

sold in the market. Also, female farmers will have more time to dedicate to their

education, health, and family with all the time saved using this mechanization.

Bibliography

"About LDCsA Propos Des Pays Les Moins Avancés - UN-OHRLLS." UNOHRLLS. N.p., n.d.

Web. 22 Sept. 2016.



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Caine, Castro, Lange & Wilkey. (2016). Design Specification of a Human Powered Peanut

Thresher

National Geographic Atlas of the World, Eighth Edition. Web. 22 Sept. 2016.

Thompson, Brian S. Creative Engineering Design. Okemos, MI: Okemos, 1997. Print.

Appendices

Figure 12: Benchmarking different types of threshing drums 1) Peg 2)Loop 3) Angle Bar

Figure 13 : Possible design for a drum inside a human powered peanut thresher



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Figure 14: A design shown with a conical drum and shaker is depicted.

Figure 15: Gear System for Powering Thresher

Figure 16: Separation System for Belt Threshing Design



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Figure 17: Fan Separation System

Figure 18: Vertical Belt Threshing System

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